Known electric grids for transmitting and/or distributing power to various loads and users are equipped with various switching devices. These switching devices, such as current interrupters or circuit breakers, have the main task of properly protecting the grid in which they are used as well as various loads and equipment connected therewith from damages which may be caused for example by electrical faults, e.g. short circuits.
To this end, a circuit breaker can include an interruption chamber with current interruption mechanisms constituted by at least one fixed contact and a corresponding moving contact. When a fault occurs, the circuit breaker can be opened by suitable actuating mechanisms which cause the movable contact to electrically separate from the fixed contact, thus interrupting the flow of current.
During opening, the mutual separation of the contacts is accompanied by the generation of an electric arc between the two contacts which should be extinguished as quickly as possible.
To face this issue, different solutions have been implemented over the years. One of the most practiced solutions uses gaseous substances such as nitrogen, noble gases, compressed air, sulphur hexafluoride (SF6) and mixtures thereof inside the interrupting chamber. But with these substances it is indispensable to use devices for monitoring the pressure of the gas used and for replenishing it in order to maintain the dielectric performance of the switching device. Further, safety systems can be adopted in order to avoid and/or indicate any loss outside the device. This arrangement affects the constructive complexity of the circuit breaker and its overall reliability.
In addition, such gases represent a major concern about environmental issues, with regard to SF6 and its negative impact on the greenhouse effect.
For such reasons, manufacturers have developed a different current interruption technology where the contacts are positioned and separate from each other inside a vacuum interruption chamber. In practice the vacuum interruption chamber surrounds a sealed space inside which a vacuum atmosphere is created and where the contacts separate.
Unfortunately, the dielectric rating of a single vacuum chamber is rather limited, e.g. up to some tens of kV, and in order to overcome such limit there have been proposed various solutions using two or more vacuum chambers or vacuum circuit breakers within the same switching device.
Clearly, such solutions using two or more vacuum chambers or circuit breakers from one side allow increasing the overall dielectric rating of the device but from the other side introduce other issues, such as complexity of the mechanisms used to actuate the various contacts, overall size of the device which may become rather voluminous and cumbersome, problems in balanced voltage sharing among the two or more vacuum chambers, or other related foreseeable and unforeseeable issues.
Examples of such known solutions are for example described in U.S. Pat. Nos. 5,347,096 and 7,550,691.
Although known solutions perform their functions in a rather satisfying way, there is still desire and room for further improvements.